The present invention is related to the field of multiple beam antenna systems and, more specifically, to a triple beam antenna system for efficiently producing three beam pointing directions without moving parts.
Offset paraboloidal antennas are commonly used in applications where good side lobe performance and good impedance matching are desired, since the offset arrangement of antenna feeds and reflector avoids the generation of side lobes due to blockage caused by an inline secondary reflector or prime focus feed.
It is well known that offset paraboloidal antennas may be provided with feeds offset from the focal point of the paraboloid when it is desired to direct the radiation field in a direction other than that produced by a feed located at the focal point. U.S. Pat. No. 3,696,435 to Zucker is one such system.
Beam steering, a changing of the direction of the radiation pattern, can be accomplished by having more than one feed point. The feed points can be switched electronically or mechanically so that the radiation can be pointed in a number of predetermined directions without physically moving the antenna. However, the amount of beam steering that can be accomplished in this manner is usually limited to less than five beamwidths due to the effect of increased coma and other aberrations which result from not operating at the focal point. More important, the smaller the displacement of the feed from the focal point, the better the directive quality of the radiation pattern. Therefore, the antenna feeds should be displaced from the focal point by as small a distance as possible.